Truman's speech after the atomic bombing of Hiroshima had multiple goals. One of the main goals was indeed to inform Japan about the devastating power of the atomic bomb. However, it was also intended to convey a message of warning and to put pressure on Japan to surrender. The speech aimed to make Japan understand the gravity of the situation and the consequences of continuing the war. So, while the speech did serve as a form of information, it was also meant to convey a strong message.